Dynamic behaviour of a fixed-bed biofilm reactor: analysis of the role of the intraparticle convective flow under biofilm growth

Abstract

The influence of the intraparticle convective flow on the dynamic response of a fixed-bed biofilm reactor is evaluated theoretically for a stepwise increase in substrate concentration in the feed line. Dimensionless transient mass balance equations for the substrate within the bulk liquid, biofilm and support phases are derived considering a substrate inhibition kinetic model (Haldane equation) and biofilm growth. Governing equations are simultaneously solved for phenol biodegradation by finite element collocation methods to yield the bed response, in terms of dimensionless phenol concentration at outlet against a reduced time (breakthrough curves), for two different bulk flow rates. The results reported in this study, for different intraparticle velocities, show that the major beneficial effect of the intraparticle convective flow on the production of a good effluent quality is expressed by the occurrence of later breakthrough curves, due to the improvement of intraparticle mass transfer by convection, particularly when higher diffusional limitations are present inside the biofilm and support. Thus, bioreactors must be operated under such conditions that liquid flow occurs within biofilms.